Non-uniform torque transmitting mechanisms such as bicycle chainwheel sets

ABSTRACT

A crank, 14, driven wheel from a central boss, 20, to an outter rim, 22, via ribs, 12 (12a or 12b), transmitting slightly improved torque to a chain (belt, rope or similar), 16, via chain wheel teeth, 10 (in this example), able to store some elastic energy in the ribs, 12, (12a or 12b), when crank, 14, transmits maximum torque (around the horizontal position) and releasing it to the rim, 22, (hence to chain, belt, rope or similar, 16,) when crank, 14, transmits least torque (around vertical positions) and having an additional ability of small elastic deformation in response to slight misalignment of the line of force offered to the rim, 22, by chain (belt, rope or similar), 16.

This invention relates to mechanisms not capable to transmit uniformtorque due to restriction imposed by the kinematic systems employed.

A classical example of such a system is the chainwheel of a bicycle withits left and right cranks and their pedals.

Each pedal subjected to a vertical downwards force applies a torque atthe centre of rotation of the crank which varies in magnitude from amaximum value when the crank is horizontal to ZERO when the crank isvertical.

Conventional transfer of this non-uniform torque from the crank to therear bicycle wheel is via a chainwheel to the rear bicycle wheel. Thislatter chainwheel has the ability of transmitting the received torqueonly clockwise and is thus called a freewheel as it does not transmittorque in the anti-clockwise direction.

This non-uniform torque is transmitted to the chainwheel twice for everycomplete rotation of cranks. The right crank during the first 180° orlast half a turn.

This invention minimises the torque non-uniformity by receiving andtemporarily storing circumferential elastic energy in the chainwheelwhen each crank delivers significant torque, energy which is almostimmediately given back to the chainwheel rim at the time when the cranksdeliver the least torque.

According to the invention a torque transmitting wheel comprising aninner ring and an outer ring and a plurality of angular spacedelastically deformable ribs, each rib being arranged such that one endis connected to the inner ring and the other end is connected to theouter ring, only said ribs providing support between said rings, saidribs allowing the outer ring to rotate relative to the inner ring whentorque is transmitted by the wheel.

Such embodiment receives and temporarily stores a circumferentialdeformation hence energy, when cranks deliver large torque and give backmost of the same energy as torque to the chainwheel rim when cranksdeliver small torque.

Extending the use of the selected polymer to almost the entirechainwheel adds advantages such as: load is shared by more chainwheelteeth than in the case of metal chainwheels; a significant weightsaving; no corrosion protection; no lubrication required; kinder to thechain; built in chainguards; generous choice of colours henceaesthetically pleasant yet remaining technically and commerciallycompetitive.

The invention will now be described in more details by way of examplewith reference to the drawings, in which:

FIG. 1 is a front view of the chainwheel showing only few teeth 10, andradial ribs 12, 12a and 12b, of the chainwheel (standard engineeringdrawing practice).

FIG. 2 is a side view of FIG. 1 with the upper half in section (SectionX--X).

FIG. 3 is part side view of a three chainwheel set in which thechainwheel teeth 10, are attachable permanently or temporarily to thechainwheel rim 22, via chainwheel rings 32, 34, and 36, directly orindirectly. It also shows the chainguard 38 attachable permanently ortemporarily to the largest chainwheel ring.

In FIG. 1 crank 14, is shown in the position where it can deliver themaximum torque to chain 16 via central metal plate 18, chainwheel boss20, radial ribs 12, 12a, and 12b, chainwheel rim 22, and chainwheelteeth 10. The choice of radial ribs geometry 12, 12a, and 12b, willdepend upon loading of chainwheels, materials and processes ofmanufacturing available and user preference, to some extent.

Chainwheel rim 22, may have the chainwheel teeth 10, integral withitself as in FIG. 1 and FIG. 2, where a single chainwheel withoutchainwheel guard is shown or attachable to itself as shown in FIG. 3that refers to multi-chainwheel embodiments.

Dotted lines 24 and 26, show grossly exaggerated the positions the teeth10, and ribs 12, 12a, and 12b, would take respectively during riding ofthe bicycle.

This position is well within the elastic limit of the material hence bythe time the crank 14 reaches the vertical position A, the elasticallydisplaced chain teeth 10 and radial ribs 12, 12a and 12b would havereturned to their unloaded normal positions. For this to take place aclockwise torque has acted on the chain 16 supporting the crank 14,which was during the stage of losing torque rapidly to ZERO.

From FIG. 2 it can be seen that the depth of radial ribs 12, 12a and 12bincrease uniformally until they reach the same depth as that of thechainwheel boss 20, that the central metal plate 18 is mouldedintegrally with the chainwheel as an insert and that there is no polymerat all in the space 28 between adjacent ribs 12, 12a and 12b.

From FIG. 3 it can be seen that the multiple chainwheel sets areemploying almost identical radial ribs 12, 12a and 12b as the singlechainwheel shown in FIG. 1 and FIG. 2 to improve the applied torquecharacteristics. It also shows chainguard 38 attached to the largestchainwheel from the set 32 attachment which can be similarly made in thecase of single chainwheel also.

For economical manufacture the central metal plate, 18, will have asmall pilot hole 30 until it is known with what configuration of crankis to be joined.

A single or multiple chainwheel set designed and manufactured to thisinvention should improve the torque transmitting characteristics of suchmechanisms.

I claim:
 1. A torque transmitting wheel comprising an inner ring and anouter ring and a plurality of angular spaced elastically deformableribs, each rib being arranged such that one end is connected to theinner ring and the other end is connected to the outer ring, only saidribs providing support between said rings, said ribs allowing the outerring to rotate relative to the inner ring when torque is transmitted bythe said ribs are cross.
 2. A torque transmitting wheel as claimed inclaim 1 wherein the ribs are integrally formed with either or both ofsaid rings.
 3. A torque transmitting wheel as claimed in claim 1 whereinthe ribs extend radially from the inner ring.
 4. A torque transmittingwheel as claimed in claim 1 wherein the ribs extend tangentially to areference circle of equal or lesser or diameter than, and concentricwith, the inner ring.
 5. A torque transmitting wheel comprising an innerring and an outer ring and a plurality of angular spaced elasticallydeformable ribs, each rib being arranged such that one end is connectedto the inner ring and the other end is connected to the outer ring, onlysaid ribs providing support between said rings, said ribs allowing theouter ring to rotate relative to the inner ring when torque istransmitted by the wheel, said ribs are S-shaped.
 6. A torquetransmitting wheel as claimed in claim 1 wherein the flexibility of theribs is such that an axis of the outer ring can deflect at an anglerelative to an axis of the inner ring.
 7. A torque transmitting wheel asclaimed in claim 1 wherein the wheel is a chainwheel.
 8. A torquetransmitting wheel as claimed in claim 7 wherein teeth are integrallyformed with the outer ring.
 9. A torque transmitting wheel as claimed inclaim 7 wherein further sets of teeth are mounted on the side of theouter ring.
 10. A torque transmitting wheel as claimed in any of claim 7wherein the chainwheel is for a bicycle.
 11. A torque transmitting wheelas claimed in claim 10 wherein a chain guard is attached to the outerring.
 12. A torque transmitting wheel as claimed in claim 11 wherein thechain guard is integrally formed with the outer ring.
 13. A torquetransmitting wheel as claimed in claim 1 wherein the ribs are formed ofa polymer.
 14. A torque transmitting wheel as claimed in claim 1 whereineither of the rings is formed of a polymer.
 15. A torque transmittingwheel as claimed in claim 7 wherein the entire chainwheel is formed of apolymer.